Here is some info I found on a website recently:
Hooking up a backup system like the one I'm using is fairly easy. It consists of two parts, an Inverter and a battery. For the inverter, I chose an Inverter/charger. By using an inverter/changer, the unit works just like a UPS when the power is cut, automatically switching over to battery. When power returns, the unit switches back to utility power and charges the battery for the next use. The unit I'm using is an APS512 from Tripplite. The unit can power up to 500 watts of equipment. For the battery, I am using a Marine, Deep Cell (sometimes called Deep Cycle) battery, it's rated at 95AH (Amp Hours). The battery was picked up from a local marine store, but you can buy them online if you do not have a boat store in your area. The combination of the two runs my Sequence 6000 pump (300 watts) for 2 1/2 hours. So far it has worked flawlessly anytime I have had a power outage, including the East coast blackout of August 14th, 2003. The only consideration you need to look into, is if you pump can take a modified sine wave for it power source. Best to call the pump manufacturer to be sure. My sequence does, as do most pumps, but you want to make sure the modified sine wave doesn't harm the pump.